TomTom Cardio Runner Review

The key feature of the TomTom Cardio Runner is its Optical Heart Rate Monitoring, rather than requiring a separate chest strap. Other than that, the TomTom does not inspire, though with the latest firmware it's fairly respectable and easy to use. You're paying a premium over some of the better watches, especially as the optical HRM does not work well. I think that the TomTom is only worth considering if you really want the built in optical heart rate monitoring, otherwise look elsewhere. For a simple evaluation of a GPS watch, I look at how well it can answer some basic questions:

How far did I run? This is the most basic question, and the TomTom now has reasonable GPS Accuracy (see below for details.)

How fast am I running? Knowing how fast you're running can be a nice to know, or it can be vital for your training or race performance. Because of the nature of GPS, watches that rely on GPS signal alone tend to have serious problems with current pace. Without the ability to display current Pace From A Footpod while getting all other data from GPS, the TomTom can't answer this question.

Where am I? The TomTom has no navigation features. (This does seem ironic from a company that specializes in GPS navigation devices.)

What's my cadence? Cadenceis one of the most critical and often overlooked aspects of running. If you get your Cadence right, many other things naturally fall into place. The TomTom has no support for Cadence.

The TomTom is not a good choice for ultrarunners, as its battery life is too short. See Watches for Ultrarunning for more details.

1 TomTom Cardio Runner Pros

The Optical Heart Rate Monitoring works reasonably well most of the time, but there are enough problems to limit its viability. Optical heart rate monitoring is a technique that has been around for decades, but it's only recently that the technology has been viable for use during exercise. The TomTom uses two green LEDs and a detector to determine Heart Rate based on the blood filling the capillaries under the skin.

When the watch has a good lock on your heart rate it's fairly accurate, and normally within a few beats/minute of a chest strap based monitor. Most of this variation seems to be due to the smoothing that's applied to the reading rather than overall accuracy.

I had a number of problems with the TomTom not locking onto my heart rate for minutes at a time. It would either show a ridiculously high or low value, so it was pretty obvious. Occasionally it would not find my heart rate at all and just show three dashes. See images below for details.

I found the problems were worse when my skin was cold. I've not tried it in winter, but at 50f/10c the TomTom struggled, probably because the capillaries it was looking for had constricted due to the cold.

Because the TomTom has to be next to the skin to monitor the blood flow under the skin, it would be problematic in winter when you need to wear extra layers of clothing. You can't put the TomTom over a base layer, so it would have to be covered by your outer layers, hiding the display.

To get a good view of your capillaries, the TomTom needs to be positioned slightly further up your wrist and to be quite tightly closed. I didn't find this uncomfortable, but it was tighter than I'd normally have a watch. However, you get a better reading with the watch tighter than is comfortable.

The TomTom will cache the locations of the GPS satellites for a few days, which worked reasonably well.

With GPS turned off, the TomTom battery will last some time, making it possible to monitor heart rate for extended periods, such as during sleep.

There is great support for automatically uploading to a variety of tracking web sites, including MapMyFitness, RunKeeper, TrainingPeaks, as well as exporting to KML, GPX, CSV, FIT or TCX files.

The TomTom can pair with a smart phone, allowing for posting of workouts or updating the satellite pre-cache via the phone.

I rather like the TomTom's four buttons arranged as a square for input, which works rather like a joystick for navigating menus. The right side of the screen is touch sensitive for turning on the backlight or recording a lap, but it's triggered by sweat.

2 TomTom Cardio Runner Cons

The core functionality of the TomTom seems rather crude when compared with other devices in this price range.

You can chose two metrics to display at the top of the screen, but these are shown in a tiny font that is hard to read in poor light.

The main display will scroll through a number of metrics, but there is little configuration of what to display. (The histogram of heart rate display is rather cool.)

The GPS Accuracy is better with the later firmware, but it looks like there is still room for improvement.

I've found no way of displaying cadence on the TomTom, which I think is a major shortfall. (There is support for a bike cadence sensor in the multisport version of this watch, but that doesn't help runners.)

This is the display layout, with two rather tiny items at the top and one rather large item in the middle. You can only configure the top row, with the main display cycling through various options.

The four buttons that surround the GPS receiver act like a joystick or joypad.

The TomTom is rather a strange shape, curving around the wrist.

The display of the Heart Rate graph, common in newer devices.

This is the first time I've seen a histogram of Heart Rate, which is rather nice.

The LEDs that detect heart rate optically. The lines you can see on the picture are not visible to the eye.

3 TomTom Cardio Runner Heart Rate Graphs

These graphs show the TomTom Cardio Runner against the record of a traditional chest strap. The top of the graph shows the two recordings superimposed, with the TomTom in red and the chest strap in blue. The lower line on the chart is the difference between the two readings.

An example run where the TomTom is showing good accuracy.

Here you can see several major discrepancies in the TomTom heart rate reading.

This run has more problems than is typical, with the TomTom repeatedly giving a bad reading.

This is an example where the TomTom is fitted tightly and gives a good reading of a High Intensity Interval Training session. The TomTom is in red and you can see that it's reading lags a little behind the chest strap. This is an extreme test, but you can see the TomTom can be out by 10 BPM, but only for a short time.

4 What's Missing

While I don't consider these missing features as 'cons', it's worth understanding the features that are missing compared with other watches.

Altimeter. GPS is far less accurate vertically than horizontally, so a barometric altimeter can provide a much better idea of your ascent and descent. It can also be useful for navigation if you're ascending or descending a mountain. In some races I've been far more interested in how much ascent is left rather than the distance to the top.

Navigation. The navigation capabilities are useful if there is a risk of getting lost. I've made good use of this feature when running in an unfamiliar city, or when running remote trails.

Downloadable Apps. Smart watches have got is used to the idea of a device that can be extended with new functionality, and this concept is being introduced to running watches.

Extended battery life. Some porches can extend the battery life by turning the GPS reception off for short periods. This can dramatically reduce GPS accuracy, but it's a useful trade-off for some ultramarathons.

Training Effect. The Firstbeat Training Effect gives you a sense of how hard each workout is, and this sometimes includes the time for recovery.

Graphs. Instead of simply displaying a numeric value for things like heart rate, some watches will display a graph of the value over time, giving you a sense of how things are progressing.

Running Dynamics. Some of the newer Garmin watches can show and record Vertical Oscillation (VO) and Ground Contact Time (GCT).

Alerts. Some watches will alert you when a metric is out of range. The alert for Cadence is really useful and one of my favorite features.

Web Configuration. Some watches allow you to setup the configuration via a web site, and then download your changes. This is vastly easier than fiddling with the watch.

5 GPS Accuracy

With the 1.8.42 or later firmware, the TomTom Runner has reasonable GPS Accuracy, but I'd expect it to do better given its use of the SIRF GPS chipset and from the tracks is creates.

The TomTom has remarkably good repeatability, which is a measure of how likely it is to give the same indicated distance on a particular part of the course. This can create an illusion of greater accuracy than is actually there, and it also suggests that the TomTom is smoothing out curves too much.

On the out-and-back turnaround the TomTom does a little worse than I'd expect for its overall rating, again suggesting too much smoothing.

Running in a straight line on the other hand, is a fairly easy task for most GPS watches, and the TomTom really excels, giving the most accurate reading of any device.

The TomTom does about how you'd expect going under the bridge.

I not had any issues with the TomTom acquiring or maintaining the GPS signal, unlike some other devices.

You can see the TomTom does remarkably well under the bridge and has no issues reacquiring the GPS signal. It does quite badly on the whole around the twisty section, cutting the corners too much due to smoothing. Interestingly, it does a better with the sharp turn seen on the right side of the diagram. Notice that the tracks are generally close together, and the lap markers in blue are very closely clustered, indicating good positional accuracy. (This diagram has tracks color coded with green indicating good accuracy through to read indicating poor accuracy, and the lap markers as blue dots.)

The earlier version of the firmware does much worse going under the bridge and around the sharp corner, but does a little better on the twisty section. This suggests to me that while they've improved the overall accuracy, they may have added in a little too much smoothing.(This diagram has tracks color coded with green indicating good accuracy through to read indicating poor accuracy, and the lap markers as blue dots.)

This close up section of a zigzag shows the tom-tom tracking nicely, with no red lines that would indicate worse accuracy.(This diagram has tracks color coded with green indicating good accuracy through to read indicating poor accuracy, and the lap markers as blue dots.)

The earlier firmware has tracks that are not significantly different from the newer firmware in shape, but you see rather more red lines and while the lap markers are tightly clustered, you see two groups, one from each direction.(This diagram has tracks color coded with green indicating good accuracy through to read indicating poor accuracy, and the lap markers as blue dots.)

Here you can see the TomTom displaying the typical GPS behavior with the tracks that have the green lines shifted slightly down and to the left, blue up and to the right. You can see the lap markers similarly shifted. (This image has the tracks color-coded for direction, with green coming from the right, blue from the left.)

The earlier version of the firmware exhibits similar behavior, though the lap markers are a little more tightly clustered, but the two clusters are further apart. (This image has the tracks color-coded for direction, with green coming from the right, blue from the left.)

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6 Visual Comparison

TomTom Cardio Runner top

TomTom Cardio Runner side

Polar M400 top

Polar M400 side

Polar V800 top

Polar V800 side

Suunto Ambit3 top

Suunto Ambit3 side

Suunto Ambit2 top

Suunto Ambit2 side

Garmin Epix top

Garmin Epix side

Garmin 920XT top

Garmin 920XT side

Garmin 620 top

Garmin 620 side

Leikr 1 top

Leikr 1 side

7 Comparison Table

I evaluate running watches in three distinct ways. Firstly, you can use a watch on its own, without any kind of Footpod. This is probably the most common way runners use their watch, but you miss out on a lot. The second rating is with a standard Footpod that is available quite cheaply. These Footpod's can be reasonably accurate once the calibrated, but calibration is a little tedious. The final evaluation is with the Stryd Footpod, which is vastly more accurate than any other type of Footpod, or and more accurate than GPS. The table below looks at the score, and the value for money of each watch for each of the three conditions. (I’ve also tested the Apple Watch 3, but I’ve not included it in these tables as it’s not really a running watch.)

The score is the sum of how well each watch can answer the four basic questions (how far, how fast, where are you, what's your cadence), plus some bonus points.

The "How far you've run" will be based on GPS only for "without Footpod" and "with Standard Footpod", but based on Stryd if supported in the "with Stryd Footpod" table..

How fast you're running assumes you're using a Footpod if it's supported, otherwise the rating is 0-2 based on GPS accuracy.

The "Where are you?" is based on various navigation features such as back to start, breadcrumbs, and preloaded maps. For some watches, you have to turn GPS off to get the benefit of Stryd, so those watches have worse "where are you scores" with Stryd than without.

The cadence score uses 1 point for an internal cadence sensor, 2 points for footpod support, 1 point for support from chest strap cadence, and 1 point for cadence alerts.

Value for money is the score divided by the price (at the time I last updated the table.) Your needs may be different, so you might weight the different aspects of the watches differently, or be basing your decision on different criteria totally. Hopefully this table will give you a good starting point for your decision.